1. Field of the Invention
The invention relates to dynamically vulcanized thermoplastic compositions having improved properties and a process for preparing the compositions.
2. Description of Information Disclosures
In recent years, there has been a significant commercial interest in polymer blends which have a combination of both elastic and thermoplastic properties. These polymer blends have been given the generic designation of Thermoplastic Olefins ("TPO"). They exhibit some of the properties of a cured elastomer as well as the reprocessability of thermoplastic resins. The elastomeric characteristics are enhanced if one component of the blend is a vulcanizable elastomer which is wholly or partially crosslinked.
The earliest work in the curing of TPO compositions was by Gessler and Haslett; see U.S. Pat. No. 3,037,954. That patent teaches the concept of "dynamic curing" wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer cured while continuously mixing and shearing the polymer blend. The result is a micro-gel dispersion of cured rubber in an uncured matrix of resinous thermoplastic polymer. Gessler's U.S. Pat. No. 3,037,954 discloses compositions comprising polypropylene and a rubber wherein the rubber may be, butyl rubber, chlorinated butyl rubber, polybutadiene, polychloroprene and polyisobutene. Compositions of about 50 to 95 parts polypropylene and about 5 to 50 parts of rubber are disclosed.
U.S. Pat. No. 3,326,833 discloses compositions of a copolymer of ethylene with an alkyl ester of an alpha-beta-monoethylenically unsaturated monocarboxylic acid, e.g., ethylene-ethylacrylate copolymer, and a halogenated olefin polymer. The rubber can be halogenated butyl rubber or chlorinated polyethylene. The compositions when uncured are thermoplastic and when peroxide cross-linked form insoluble non-thermoplastic resins.
U.S. Pat. No. 4,639,487 discloses heat shrinkable thermoplastic composition of an ethylene copolymer resin with a dynamically vulcanized halogenated butyl rubber.
Dynamically vulcanized compositions comprising a crystalline thermoplastic olefinic resin and a butyl rubber are known. See, for example U.S. Pat. No. 4,130,534.
U.S. Pat. No. 4,350,794 discloses a polyamide molding and extrusion composition prepared by melt blending a polyamide resin and an elastomer having a polyamide reactive halogen functional group which may be a parahalomethylphenyl group.
There is still a need to improve the properties of dynamically vulcanized compositions.
It has now been found that dynamically vulcanized compositions comprising a thermoplastic olefinic resin and a elastomeric halogen-containing copolymer of an isoolefin and a para-alkylstyrene have improved properties.